St. Mary's Avenue - that was the prior name of De Reimer Avenue, back in 1905. Many streets in Baychester back in the old days had different names. I don't know when it got renamed to De Reimer Avenue. De Reimer Avenue was named after a merchant of Dutch ancestry: Isaac De Riemer, who became the 25th Mayor of New York City from 1700-1701. I don't know how the name De Riemer/De Reimer name came to be spelled differently!
This street once was a continuation of the De Reimer Avenue that still exists in the larger Baychester neighborhood, before the Hutchinson River Parkway was built and cut this village off from the rest of Baychester. After being cut off it lived in the village as a one-block street, situated between Bassett and Stillwell Avenues.